1. Field of the Invention
The present invention relates to a rolled material temperature control method for the delivery side of a rolling mill and the rolled material temperature control equipment thereof.
2. Description of the Related Art
Hitherto, in order to obtain the material properties of the product, such as tensile strength regarding hot rolling, it has been a requirement that the material temperature at a position on the delivery side of the rolling mill should accurately meet a designated target value over the whole length of the material. To adjust the material temperature at the position on the delivery side, there is a method of controlling the cooling water flow of inter-stand cooling equipment as a coolant and a method of controlling the rolling speed. Normally, these two methods have been used in combination.
Temperature control means for making the material temperature at a position on the delivery side of a rolling mill meet a target value have been disclosed in Laid-Open Patent Gazette No. Heisei 7-75016, Laid-Open Patent Gazette No Heisei 8-150409 and Laid-Open Patent Gazette No. Heisei 10-94814. All of these prior art techniques have compositions that make the temperature on the delivery side of the rolling mill meet the target value by first determining the rolling speed variation pattern, and then, taking this speed variation pattern as a constraint condition, calculating the cooling water flow at each position in the longitudinal direction of the material and controlling the cooling water flow according to the calculated values.
FIG. 2 is a typical rolling mill speed variation pattern. The rolling speed (the roll peripheral velocity of final stand N of the rolling mill) is caused to vary in the three stages of threading speed V.sub.N1, running speed V.sub.N2 and tall out speed V.sub.N3. With the prior art technology, as a general rule, firstly, speeds V.sub.N1, V.sub.N2 and V.sub.N2, are, for example, pre-determined by retrieving the value stored in tables or the like, and then, taking these as constraint conditions, the inter-stand water flows are calculated.
Also, when controlling the above-mentioned cooling water flows and rolling speeds, it is necessary to calculate the appropriate control quantities using a mathematical model (hereafter called `temperature model`) that can accurately simulate the temperature variation behavior of the material in the rolling mill. For this purpose, there is a requirement to consider the following factors in the temperature model.
(a) Processing heat generation accompanying material deformation at each stand PA1 (b) Frictional heat generation due to relative slip of the contact surfaces of the material and the rolls PA1 (c) Heat loss from the contact surfaces of the material and the rolls PA1 (d) Heal loss due to thermal radiation to atmosphere from the material surface between the stands PA1 (e) Heat loss to cooling water from the material surface between the stands
Examples that take these factors (a).about.(e) into consideration in each of the calculations of the above-mentioned threading speed V.sub.N1, running speed V.sub.N2 and tail out speed V.sub.N3 are few. However, that published in Laid-Open Patent Gazette No. Heisei 10-94814 can be considered these factors.
In prior art material temperature control methods such as the above, it is necessary for an operator or an engineer to determine the rolling speed based upon experience. Nowadays it is desirable to increase the rolling speed in order to increase productivity. However, in cases of increasing the rolling speed, there are some cases in which the cooling water flows of the inter-stand cooling means are insufficient due to the constraints of the equipment. In other words, because the set speed value is excessive in relation to the useable cooling water flow, in particular, the cooling water flow being insufficient immediately after acceleration from threading speed to running speed, etc., that part of the rolling mill delivery side temperature relevant to the lengthwise direction of the material will not meet the target value.
Consequently, in order to obtain high productivity while guaranteeing the rolling mill delivery side temperature, it was necessary to determine the most appropriate rolling speed (principally, the above-mentioned running speed V.sub.N2). This work was mainly done by trial and error on the operator's or engineer's part. For that reason, there were the problems that a great deal of labor was required and that waste of material and energy occurred.
Moreover, in cases where the material temperature at the entry side of the rolling mill or the material thickness at the entry side of the rolling mill changed, it was necessary to re-determine the most appropriate set speed value a second time, and the above-mentioned problems continuously occurred while the operation of the rolling mill continued.
In order to solve such problems, a method can be considered of determining the cooling water flows at a rolling speed variation point, and then calculating the speeds for each section of the speed variation pattern, taking these cooling water flows as constraint conditions. When using this method, the most appropriate rolling speed for a given cooling water flow can easily be determined. Therefore, it becomes possible to make the material temperature at a specified position on the rolling mill delivery side meet the target temperature with good accuracy over the entire length of the material, while guaranteeing high productivity.
However, of the various factors used in the above temperature model, factors (a) and (b) are based upon the deformation resistance of the material, and when the rolling speed is altered, the deformation resistance will change due to the change in the strain rate. Therefore it is necessary to take into consideration the point that these quantities of heat generation will also vary. In other words, in the case of calculating rolling speed taking cooling water flow as a constraint condition, convergence calculation becomes necessary concerning speed.